Almost 30,000 coronary artery bypass graft procedures are perfomed each year in the UK according to the British Heart Foundation, however over 50% of CABG fail within 10 years due to the development of neo-intimal hyperplasia.
#Coronary artery bypass surgery, also coronary artery bypass graft (CABG pronounced cabbage) surgery, and colloquially heart bypass or bypass surgery is a surgical procedure performed to relieve angina and reduce the risk of death from coronary artery disease. Arteries or veins from elsewhere in the patient's body are grafted to the coronary arteries to bypass atherosclerotic narrowings and improve the blood supply to the coronary circulation supplying the myocardium (heart muscle). This surgery is usually performed with the heart stopped, necessitating the usage of cardiopulmonary bypass; techniques are available to perform CABG on a beating heart, so-called "off-pump" surgery.
#Intimal hyperplasia is the thickening of the Tunica intima of a blood vessel as a complication of a reconstruction procedure or endarterectomy. Intimal hyperplasia is the universal response of a vessel to injury and is an important reason of late bypass graft failure, particularly in vein and synthetic vascular grafts.
Similiarly, arterio-venous shunts constructed from ePTFE are prone to occlusion by thrombosis and intimal hyperplasia.
In the US alone there are 175,000 ePTFE grafts used for permenant vascular access, with the 1 and 2 year primary patency rates currently at 50 and 25% respectively.
Consequently, much research has been conducted in the past few decades to design drafts that will remain patent for far longer, ideally longer than the life-span of patient.
A promising avenue of this research, initiated by Caro and co-authors, is to use out-of-plane geometry that induce fully three-dimensional, physiologically realistic swirling flows, and produce more uniform wall share stress distributions. However in a clinical environment, such geometries cannot be guaranteed to be preserved after wound closure. Greater control of geometry is possible with vascular prostheses, with small amplitude helical tubes being proposed. The helical geometry induces the necessary swirling flow, whilst also being mechanically robust, and has undergone preliminary in vivo trials, and subsequently a preliminary clinical study by Huijbregts el al. Caro et al. hypothesized that the in-plane mixing induce by the helical geometry and the more uniform WSS distribution are responsible for preventing graft occulasion from thrombosis and neo-intimal hyperplasia.
Likewise a new design of arterial stent has been proposed which when inserted in the host artery and expanded, enforces a helical tube boundary at the artery wall. This is an alternative procedure to the helical bypass graft, but the operating conditions, e.g Reynolds number, will be comparable to those of bypass graft. It is to be emphasized that the benefits of helical geometry in vascular conduits have yet to be firmly estasblished, although they appear promising. The range of possible configurations is large, and how the hemo-dynamics responds to changes in geometric parameters has not been studied in detail.
Systematic investigation of the effects of helical geometry on the hemodynamics are needed, not only to inform potential design of prostheses and surgical vascular reconstructions, but to improve our understanding of normal vasculature. As pointed out by Zabielski and Mestel, a helical pipeserve the idealization of many arterial geometries. The mechanisms governing mixing in such geometries may provide insiht into cardiovascular diseases such as atheroclerosis, which are thought to be linked to wall shear stress and wall transport. These consoderations provide the motivations for the work described below, in which a range of small amplitude helical geometries, representative of possible prosthetic vascular configurations or native tortous arteries are the subject of studies of flow structure and mixing.
#arterio-venous-A/V
#shunt- a hole or passage allowing fluid to move from one part of the body to another
#stent- is an artificial 'tube' inserted into a natural passage/conduit in the body to prevent, or counteract, a disease-induced, localized flow constriction. The term may also refer to a tube used to temporarily hold such a natural conduit open to allow access for surgery.
#hemodynamics- meaning literally "blood movement" is the study of blood flow or the circulation
#prostheses- a prosthesis, prosthetic, or prosthetic limb (Greek: πρόσθεσις "addition") is an artificial device extension that replaces a missing body part.
#tortuous- full of twists and turns.
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